When a subsea well is completed, it is important to be able to monitor the annulus cavity between the tubing and the innermost casing string for leaks and yet also to be able to shut in the annulus cavity, if needed. One method to accomplish this is to provide a second vertical throughbore to the tubing hanger and change the single bore subsea tree to a dual bore subsea tree. This approach may be expensive since the cost of the subsea tree increases significantly and a second riser string needs to be run with the hanger and the tree.
Another way to accomplish this is to put a valve to the hanger, thereby reducing the cost of the dual tree to that of a single bore tree. There have been various hanger valves designed in the past, including annulus valves and small bore gate valves. These valves are of limited use in that a long life, conventional metal-to-metal seal is problematic. Moreover, this approach typically restricts the gate valve flow bore diameter to 1″ and greatly increases the hanger length. The disadvantages of the prior art are overcome by the present invention, as described in more detail below.
Prior patents include U.S. Pat. Nos. 6,729,392, 6,453,944, 6,626,239, 6,520,207 and 6,497,277. The '944 patent discloses a gate valve assembly with an actuator for moving gates simultaneously. The '277 patent discloses a gate valve with a return housing mechanism.